Results 1 to 9 of 9

Thread: Branch Circuit Feeders

  1. #1
    Join Date
    Aug 2013
    Location
    new york
    Posts
    8

    Branch Circuit Feeders

    Hey Forum

    I am installing a 277/480 service and have a question on wire size.

    Long Island

    Coming off main service in shopping center and feeding a Trans S Meter Cabinet
    Than installing 200 amp / 600 volt Safety switch. 6x6 x4 rain tight trough
    Going to fuse switch down to 150 amp ??
    I have too run 400 feet to supply and 480 step down transformer. Stepping down to 120/208.
    This 120/208 panel are main breaker at 150 amps
    I was looking up wire size and at 3% I could run 1/0

    The question
    Do I have to run full size 1/0. Which is good up to 427 feet at 480 volt delivering 150 amps at the end, or Can I run wire size that is 80 percent of the 150 main breaker in the 120/208 panel

  2. #2
    Join Date
    Jan 2009
    Location
    Maryland
    Posts
    11,421
    Quote Originally Posted by zodiack View Post
    ....Can I run wire size that is 80 percent of the 150 main breaker in the 120/208 panel
    I am confused at what you are asking.

    80% of 150A = 120A and a 120A conductor would need to be protected with a 125A breaker.
    "Electricity is really just organized lightning." George Carlin


    Derek

  3. #3
    Join Date
    Aug 2013
    Location
    new york
    Posts
    8

    Wire Size

    I know I can run 1/0 wire

    Can I size the wire 80 percent of the 150 amp breaker

    In turn using a 125 amp fuses in disconnect switch down sizing the wire. to #1 wire

  4. #4
    Join Date
    Jan 2009
    Location
    Maryland
    Posts
    11,421
    Quote Originally Posted by zodiack View Post
    I know I can run 1/0 wire

    Can I size the wire 80 percent of the 150 amp breaker

    In turn using a 125 amp fuses in disconnect switch down sizing the wire. to #1 wire
    Isn't that disco on the primary side of the transformer that is in turn feeding the 150A panel?
    "Electricity is really just organized lightning." George Carlin


    Derek

  5. #5
    Join Date
    Jan 2009
    Location
    Maryland
    Posts
    11,421
    This whole idea of sizing a conductor to 80% of a breaker makes no sense to me.

    This what a typical tranny set up looks like:

    480V to 208/120V

    Name:  207ecm24fig1.jpg
Views: 174
Size:  80.3 KB
    "Electricity is really just organized lightning." George Carlin


    Derek

  6. #6
    Join Date
    Jan 2014
    Location
    ny,ny
    Posts
    48
    Agreed jumper...where is this sizing the wire to 80% of the OCPD coming from? Is it a misunderstanding of not designing to use more than 80% of a circuits rating? Im confused but no you can't undersized the wire to 80% of the OCPD. In the transformer diagram, I'd prob parallel the secondary instead of 700kcmil but correct as it stands.

    Sent from my SM-G935P using Tapatalk

  7. #7
    Join Date
    Dec 2012
    Location
    Placerville, CA, USA
    Posts
    17,636
    You can sort of size the wire to 80% some of the time as follows:
    If the load can only be 80% of the breaker rating, then you can size the wires to the load and then possibly use the larger breaker as the next size up from the load current.
    Or, depending on the load, you might have to size the wire all the way up to the breaker size to satisfy the 80% rule for the breaker.

    Sent from my XT1585 using Tapatalk

  8. #8
    Join Date
    May 2012
    Location
    Amissville, Virginia USA
    Posts
    148
    Quote Originally Posted by jumper View Post
    This whole idea of sizing a conductor to 80% of a breaker makes no sense to me.

    This what a typical tranny set up looks like:

    480V to 208/120V

    Name:  207ecm24fig1.jpg
Views: 174
Size:  80.3 KB
    80 % is for future expansion. i believe the code states that some where i will look at it when i get a chance.

    Sent from my SM-T350 using Tapatalk

  9. #9
    Join Date
    Jan 2009
    Location
    Maryland
    Posts
    11,421
    Quote Originally Posted by Daniel malack View Post
    80 % is for future expansion. i believe the code states that some where i will look at it when i get a chance.

    Sent from my SM-T350 using Tapatalk
    You can look, but you ain't gonna find it.
    "Electricity is really just organized lightning." George Carlin


    Derek

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •